1. Field of Invention
The present invention generally relates to network communication systems, and more particularly, to systems and methods for transcoding multimedia information within a network communication system.
2. Description of Related Art
Multimedia information, such as audio and video, has become a common and increasingly popular form of content transmitted across modern communication networks. In fact, many applications, such as web browsers, media players and digital jukeboxes, have been specifically developed to allow users to download multimedia information from variety of sources and play or display such information on demand. Content providers have also developed a variety of services that enable users to download music, video programming and other information rich content in real time using, for example, sophisticated streaming or multicasting technology. With the predicted increase in demand for such services, multimedia information will likely constitute a significant portion of the data traffic communicated over network communications systems in the future.
This increased demand for multimedia information, however, has highlighted a number challenges associated with the transmission of such information over conventional network communication systems. These challenges stem from the fact that multimedia information is typically encoded at the source at a predetermined transmission rate, with the assumption that the communication channel will always have sufficient bandwidth to support the rate at which the multimedia information is encoded. If multimedia information is encoded at a transmission rate that is greater than the available transmission rate, however, the receiver may be unable receive information at the rate necessary to support the underlying application, thereby causing the application to experience disruption or significantly degraded performance.
These problems have become especially apparent in wireless and other bandwidth constrained networks. Because these networks have physical limitations on the maximum bandwidth that the communication channel can support (which in many cases may be significantly less than the bandwidth supported by conventional wireline links), the assumption that the communication channel will always have sufficient bandwidth to support the required transmission rate may not apply. As a result, these bandwidth constrained networks are susceptible to a mismatch between the required transmission rate of the multimedia information and the available transmission rate of the communication channel. Wireless networks are especially problematic due to the temporary decreases in the available transmission rate caused by rain fades, multipath fading, call handoff, degradation in signal quality and other commonly occurring phenomenon that decrease the available bandwidth.
Conventional TCP architectures employed in data communication networks further exacerbate the foregoing problems by failing to take into account the asymmetric uplink and downlink channels typically employed in wireless and other bandwidth constrained networks. For example, conventional TCP flow control mechanisms utilize an acknowledgement-based approach to regulate the number and timing of new packets transmitted over the communication network. In these implementations, a transmitter maintains a congestion window parameter that specifies the maximum number of unacknowledged packets that may be transmitted to the receiver. As the transmitter receives acknowledgement signals from the receiver, the congestion control mechanism increases the size of the congestion window (and decreases the number of unacknowledged packets), thereby enabling the transmitter to immediately transmit additional packets to the receiver.
The problem with this approach is that it assumes that the network employs symmetric uplink and downlink communication channels that enable data packets and acknowledgement signals to be equally spaced in time. In communication networks, such as wireless communication networks, that employ asymmetric uplink and downlink channels, the available bandwidth towards the receiver may be significantly higher than the available bandwidth towards the transmitter. As a result, the receiver may be unable to access the uplink channel in order to transmit acknowledgement signals to the transmitter in a timely manner. This initial delay in the transmission of acknowledgement signals may cause the transmitter to suspend transmission of additional data packets until additional acknowledgement signals are received, and then transmit a large burst of packets in response to the transmitter receiving a large group of acknowledgement signals. As a result, these acknowledgement-based approaches may underestimate the available transmission rate on the downlink channel and result in data being transmitted to the receiver in large bursts, thereby causing multimedia applications requiring a steady flow of data at a predetermined transmission rate to experience unusually poor performance.
Therefore, in light of the problems associated with existing approaches, there is a need for improved systems and methods for communicating multimedia information over a network communication system.